Abrasion of caking

ABSTRACT

In a system for the manufacture of cement having a preheater for preheating raw material fed to a heated rotary kiln, a method is disclosed for removing caked raw material from internal wall areas of the preheater which are likely to build up such caked material. The method relates to suspending cement clinker particles in a gas moving at a high velocity and causing the gas and particles to impinge upon the wall areas which are normally subject to caking at sufficient velocity to dislodge the caking.

United States Patent 1 1 1111 3,831,326 Albertus Aug. 27, 19 74 ABRASION 0F CAKING 1,058,298 4/1913 Gregg 51/319 ux 1,795,348 3/1931 Schmidt.... 51/320 UX [751 "Y Gundol'ph Albert, 2,665,118 1/1954 Broman 51/320 x Copenhagen-WM, Denmark 3,207,494 9/1965 Jager 1; 263/21 A [73] Assignee: F. L. S midth & Co., New York.

Primary Examiner-Donald G. Kelly [22] Filed: Oct. 25, 1972 Attorney, Agent, or Firm-Pennie & Edmonds [21] Appl. No.: 300,457

Related US. Application Data [57] ABSTRACT [62] Division of Ser. No. 807,852, March 17, 1969, Pat.

No. 3,726,045. I '1 w I WM In a system for the manufacture of cement having a 30 F A preheater for preheating raw material fed to a heated 1 orelgn pphcauon, prlomy Data rotary kiln, a method is disclosed for removing caked Mar. 20. 1968 Great Britain 13455/68 raw material from internal wall areas of the preheater which are likely to build up such caked material. The [2%] $5.31. 515232614321 method relates to suspending cement clinker particles 1 .1 in a g moving at a i y and causing g 1 o arc l3 2 and particles to impinge upon the wall areas which are t l References Cited igairgatlggsrfiiercgto cakmg at sufficient velocity 0 1s UNITED STATES PATENTS 782.608 2/l905 Jackson 5l/3l9 UX 3 Claims, 4 Drawing Figures l4 l5 l2e I40 15a 6 4b PAIENTEflnuszmn SHEET 10$ 2 FIG. I

FIG. 2

PAIENTED 3.831 .326

WEE-I 2 BF 2 FIG. 3

ABRASION or CAKING CROSS REFERENCE TO RELATED APPLICATIONS The present application is a divisional of co-pending application Ser. No. 807,852 filed Mar. 17, 1969, now U.S. Pat. No. 3,726,045. r

BACKGROUND OF THE INVENTION In the cement industry and allied industries granular raw material burnt or sintered in a rotary kiln is commonly preheated before entering the kiln by contact with hot gases in a suspension preheater. This may consist of a series of cyclones connected to one another and to the kiln by pipes, the material being carried upwards in suspension by the hot gases to each cyclone through a riser pipe and entering the kiln from the last cyclone; or again a suspension preheater may consist of a shaft constructed so that some at least of material introduced into the top of it moves downwards against the rising hot gases as a result of being formed into aggregates or dense clouds by circulating gas currents in the shaft or in chambers or sections into which the shaft is directed.

It is often found that the raw material tends to cake on surfaces inside a suspension preheater, the resultant cakes giving rise to serious difficulty in operation. This occurs in practice when the gases contain alkali vapours and chlorides normally of alkali metals. The ob jective of this invention is to solve this problem.

I SUMMARY OF THE INVENTION Caking is prevented or removed, according to the invention, by abrading the surfaces with solid particles or atomised water either continuously or intermittently.

The abrasion may be effected by bombardment with solid particles, the process then being similar to the removal of oxide from metal surfaces by sand blasting; or by bombardment with water, the process then being similar to the cleaning of stone buildings; or by allowing solid particles to fall under gravity onto or in contact with the surfaces. In each case there is not only abrasive action, but'also some cooling which produces temperature differences in cakes already formed so that internal stresses are set up on these and cause them to break.

The abrading material must not, of course, interfere with the burning or other process in the kiln or damage the product. If water is used, it will immediately evaporate in the normal preheater, and thus never enter the kiln. If the abrading material is solid, it may most advantageously be particles of the raw material or of the final product. Thus, in the burning of cement, the abrading material may be cement raw meal which may be in the form of nodules, or cement clinker, which may be crushed to some extent or may constitute a fraction from a sieving process to which the clinker may be subjected. Raw meal as such is rather soft andsize. If the abrasion is effected under the influence of I gravity, larger particles, say from 5 to mm in size, should be used, such for example, as nodules of cement raw meal.

Naturally only those surfaces on which there is a tendency for cakes to form are abraded. The invention is primarily concerned with suspension preheaters for cement raw meal, and is particularly applicable, although not limited, to cyclone preheaters. These usually comprise several stages, for example four, and generally there is a tendency to caking only in the hottest stage, i.e., that nearest the kiln, and in the pipes between it and the kiln.

Apparatus for carrying out the method may take various forms. If the abrading material is to bombard the surface, pipes terminating in appropriately directed nozzles may be passed through the walls of the cyclones i and pipes. If the abrading material is water, it may be supplied to all these pipes through a single main pipe by a water pump. If the abrading material is a solid, means are preferably provided for introducing it individually into each pipe close to the wall of the cyclone or pipe. These means may advantageously be a hopper and a dosing valve, which can be operated continuously or intermittently as required.

Alternatively, appropriate openings may be made in the walls of the preheater and be closed by cover plates, which can be removed easily when cakes are to be bombarded. Then a suitable apparatus including a flexible pipe with a nozzle can be brought into position so that the nozzle enters each opening in turn, and the internal surfaces are bombarded with water or solid particles through the nozzle.

If the abrading material is to fall under gravity into a cyclone or down a pipe, there may be a supply hopper and valve at each of a number of openings around the top of the cyclone, or around the pipe at a point where it is reduced in cross-seciton so that material introduced vertically through the openings will move down the inner surface of the part of the pipe below. Again, at the top of a cyclone a ring carrying a hopper and dosing valve mounted above an opening in the ring may be arranged to rotate around the vertical axis of the cyclone so that the abrading material is discharged from the opening into contact with the surface below throughout the rotation.

Two forms of apparatus according to the invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which:

FIG. 1 shows the lowermost stage of a cyclone preheater connected to the upper end of a rotary kiln and provided with means for bombarding various surfaces;

FIG. 2 shows a detail of FIG. 1 on an enlarged scale;

FIG. 3 shows the lowermost cyclone of a cyclone preheater provided with means for feeding abrading material under gravity and FIG. 4 shows the parts indicated at B in FIG. 3 on an enlarged scale.

FIG. 1 shows the upper end of a rotary kiln 1, the

' mouth of which is surrounded by a casing 2 which joins a riser pipe 3. The riser pipe 3 opens tangentially into a cyclone 4, from the top of which a central gas pipe 5 leads to the next stage of the preheater. Preheated raw meal separated from gas in a cyclone (not shown) in the next stage flows down a pipe 6 to enter the riser pipe 3 and is entrained by thehot gases coming from the rotary kiln, with the result that the temperature of the meal will rise further. The gases carry the rawmeal into the cyclone 4, which has a cylindrical part 40, which joins onto a conical part 4b which in turn joins onto a cylindrical part 4c, the lower end of the cyclone being formed by a conical part 4d. In the cyclone 4 the preheated raw meal is separated, leaving the bottom of the cyclone through a down pipe 7 under the control of a device 8 which serves to ensure that raw meal may pass down through the pipe 7, while preventinggas from passing through it. The pipe 7 discharges into an inclined pipe 9 by means of which the preheated raw meal is fed into the rotary kiln 1 through the casing 2. The gases leave the cyclone through the pipe to enter the cyclone in the next stage, entraining further raw meal in their passage.

lf the hot kiln gases contain alkali vapours or chlorides, there is a tendency to caking. The reason is that these condense on dust and raw meal particles entrained in the gases, the surfaces of these particles become sticky, and some of them adhere to the inner walls of the riser pipe 3 and the cyclone 4; and the cakes formed on these walls form the seats of new sticky particles, and so on.

One of the devices for counteracting caking is shown in FIG. 2, in which 10 denotes a part of the wall of a riser pipe or a cyclone. A pipe 11 passes through the wall 10 and terminates in a nozzle 12 directed downwardly and inwardly towards the wall. Similar pipes 11 are provided at appropriate angular spacing, for example 90, around the cyclone or pipe, and are all connected to a circular pipe 13 which surrounds the cyclone or pipe and through which compressed air is fed to the pipes 11. Solid abrading material is fed into each pipe 11 from a hopper 16 (not shown in FIG. 2) under the control of a valve 15, which may be any suitable kind of dosing valve.

In a cyclone preheater caking is found to occur particularly in the conical part of the lowermost cyclone, in the riser pipe to that cyclone, on the outer wall of the curved part of this riser pipe that leads to the cyclone and on that wall of the casing 2 which is struck by the gases from the kiln. Accordingly circular pipes, each with its radiating pipes 11 and nozzle 12, are provided at 13a around the bottom of the part 4a of the cyclone and at 13b around the bottom of the part 46. the nozzles being downwardly directed so as to bombard the surfaces at the upper ends of the parts 4b and 4d respectively. Circular pipes 130 and 13d are provided around the riser pipe 3, the nozzles on the radiating pipes fed by the pipes 130 and 13d being downwardly directed. To counteract caking on the curved part of the riser pipe, a single, upwardly directed nozzle l2e is provided. Finally a single nozzle 12f is downwardly directed to bombard the wall of the casing 2.

The number of nozzles required at any point depends largely on the tendency to caking. As shown, each of the circular pipes 13a and 13d feeds three nozzles and the circular pipes 13b and 130 each feed four nozzles. To reduce the number of containers 16 two nozzles may have a common container 16. On the other hand, the distance between the container and the nozzle should be short.

The abrading material is entrained in the gases, separated from them in the cyclone 4 or in a higher stage and finally fed to the kiln through the pipe 9.

The cyclone shown in FIG. 1 is of somewhat unusual shape, the reason being that this shape enables the nozzles to be mounted particularly conveniently for the purpose of keeping the lower part of the cyclone free from cakes.

FIGS. 3 and 4 show the lowermost cyclone 4 of a cyclone preheater, this cyclone consisting only of an upper cylindrical part 4a and a lower conical part 4b. The cyclone is fed by a riser pipe 3 and the gases are discharged from it through a pipe 5. An annular shoulder 33 exists at the top of the cyclone around the pipe 5, and close to the edge of this an annular depression 21 is formed. At the base of this depression there is a slot 22 giving access to the interior of the cyclone. This slot extends all the way around along the circumference of the cyclone, interrupted at a few points only by bridges (not shown) ensuring connection between the central part of the cover and its outer edge.

A ring 23 fits loosely into the depression 21 and has a single opening which registers with a pipe 24 carrying a dosing valve 25. The pipe 24 is connected to a container 26 containing nodules of raw meal or particles of clinker. The container 26 is carried by a frame 27 which is supported by and mounted to turn round the pipe 5. This frame includes two rings 28 and 29 which mate with sliding surfaces on the pipe, the ring 28 resting on an annular flange 32 that is rigid with the pipe. A gear rim 30 is fixed to the pipe and is engaged by a pinion 31, which is driven through a reducing gear train 35 by a motor 34 carried by the frame 27. Rotation of the motor thus causes the frame 27 to rotate slowly around the pipe 5, carrying the container 26 with it. In the course of one revolution the pipe 24 passes through the entire slot 22 so that nodules or clinker grains from the container 25 will fall very heavily and closely along the inner wall of the cylindrical part 4a of the cyclone and subsequently trickle down the conical part 4b, with the result that the walls of both parts are kept free from caking. The nodules should be sufficiently large and heavy that they will be little affected by the gas circulating in the cyclone.

The single rotating container 26 may be replaced by several stationary containers uniformly distributed around the top of the cyclone. In this case an opening is provided in the top of the cyclone for the pipe 24 leading from each container 26. However, this construction does not give the same uniform attack by nodules over the whole circle of the cyclone that is given by a rotating container.

It will be understood that the foregoing description relates to specific embodiments of the invention and is merely representative. In order to appreciate fully the spirit and scope of the invention, attention is invited to the appended claims.

1 claim:

1. A method of counteracting caking tendencies in a suspension preheater, such as cyclone preheater, which feeds a rotary kiln with preheated cement raw meal so as to be burnt to cement clinker, comprising: suspending cement clinker particles in a gas moving at a high velocity, said cement clinker particles having no detrimental influence upon the burning process in the rotary kiln or upon its product; causing said gas and particles to impinge upon internal wall areas of the preheater which are normally subject to caking at sufficient velocity to dislodge the caking; permitting these particles to exit from the preheater together with preheated cement raw meal exit flow; and feeding said particles to the kiln together with said preheated cement raw meal exit flow.

2. The method according to claim 1 further compris- 3. The method according to claim 2 further comprismg intermittently suspending said cement clinker partiing suspending cement clinker particles which are cles in said gas moving at a high velocity thereby intermittently dislodging caking on said internal wall areas of said suspension preheater. 5

proximately in the order of about 2 mm in size. 

1. A method of counteracting caking tendencies in a suspension preheater, such as cyclone preheater, which feeds a rotary kiln with preheated cement raw meal so as to be burnt to cement clinker, comprising: suspending cement clinker particles in a gas moving at a high velocity, said cement clinker particles having no detrimental influence upon the burning process in the rotary kiln or upon its product; causing said gas and particles to impinge upon internal wall areas of the preheater which are normally subject to caking at sufficient velocity to dislodge the caking; permitting these particles to exit from the preheater together with preheated cement raw meal exit flow; and feeding said particles to the kiln together with said preheated cement raw meal exit flow.
 2. The method according to claim 1 further comprising intermittently suspending said cement clinker particles in said gas moving at a high velocity thereby intermittently dislodging caking on said internal wall areas of said suspension preheater.
 3. The method according to claim 2 further comprising suspending cement clinker particles which are approximately in the order of about 2 mm in size. 